Interesting possibilites for the US Air Forces Aircraft

The Solar Impulse project aims to have a plane powered exclusively by solar energy take off and fly autonomously, day and night, to the point where it could circumnavigate the globe with no fuel, generating no pollution.
The pilots of the Solar Impulse, Bertrand Piccard, psychiatrist/adventurer, and André Borschberg, pilot/entrepreneur, have been leading the project since 2003. Beginning with the first flights, they will share the missions, as at the moment the aircraft can only carry one pilot at a time.
AERODYNAMIC
The wingspan of the aircraft measures 80 metres, slightly wider than the wingspan of an Airbus A380, in order to minimise drag and offer a maximum surface for solar cells. Such light wing loading (8 kg/m2) creates greater sensitivity to turbulence. The ultra-light structure must use customised carbon fibres.
Max. altitude
12,000 m
Max. weight
2000 kg
Average speed
70 km/h
Wingspan
80 m
Max. power of motors
35 kW
Battery weight
450 kg
Battery capacity
200 Wh/kg
Photovoltaic efficiency
0.2


http://en.wikipedia.org/wiki/Solar_Impulse




My question is this; Why isn't the military investing in solar powered aircraft? The effiency of these particular solar cells of course is terrible but as technology moves on maybe we will see enhanced 20 percent efficient solar cells on planes. This technology has a lot of potential to reduce the Air Force's fuel consumption. Right now the most efficient solar cells can transfer 40 % of the suns energy that hits them in to useable power. The potential savings are enormous, projects like this need more attention and I think the Air Force is a perfect example that can get more interest in solar powered planes.